Steam is effectively used in power stations and factories as a heat source and a pressure source. Metal pipes manufactured from stainless steel or chromium steel are employed for steam distribution. Such metal pipes suffer from creep damage when steam is at high temperature and high pressure, for example, in cases where the steam temperature is several hundreds of degrees Celsius, and the steam pressure is several Mpa.
Thus, when metal pipes are large diameter pipes employed for motive steam used in turbines or the like, in cases in which, for example, the pipe has a diameter of several hundred mm, creep voids develop in the surface of the metal pipe due to creep damage, and the number and surface area of the creep voids increase with the progression of creep damage. Remaining service life evaluation methods, such as an A parameter method or an M parameter method, have been proposed that take into consideration the characteristic way in which the number and surface area of creep voids increase (see Patent Documents 1 and 2).